The primary English meaning of "canard" comes from the Medieval French expression “vendre un canard à moitié”, which literally means “to sell half a duck” or “to half-sell a duck”. This was perhaps the punch line to a joke. Eventually the punch line came to stand for the joke and then finally the word alone stood for the whole concept. The story may perhaps have gone like this: A duck seller is successful and content as the only duck seller on a street, selling his ducks for eight francs each. A new duck seller moves in across the street who steals all the business by offering his ducks for seven francs each. Then a price war ensues, back and forth, until the new duck seller is down to three francs for a duck. The original duck seller is beside himself with worry and frustration, but finally he puts up a big sign that says, “Two francs” and then in small print at the bottom “for half a duck.” In this way, to half-sell ducks may have come to mean tricking people with something that is literally true but misleading. It has this same metaphorical meaning in French. Now in English, it simply means anything that is deliberately misleading, a hoax.

It’s a cinch, now that Spurling has cleared away a century’s worth of misapprehensions and canards.

2014 August 20, “Why Jews are worried [print version: International New York Times, 22 August 2014, p. 8]”, in The New York Times‎[1]:

[W]hen a Hamas spokesman recently stood by his statement that Jews used the blood of non-Jewish children for their matzos – one of the oldest anti-Semitic canards around – European elites were largely silent.

(aeronautics) A type of aircraft in which the primary horizontal control and stabilization surfaces are in front of the main wing.